docs: def handle_namespace_url(self, line: str, position: int, tokens: ParseResults) -> ParseResults:
          """Handle statements like ``DEFINE NAMESPACE X AS URL "Y"``.
  
          :raises: RedefinedNamespaceError
          :raises: pybel.resources.exc.ResourceError
          """
          namespace = tokens['name']
          self.raise_for_redefined_namespace(line, position, namespace)
  
          url = tokens['url']
          self.namespace_url_dict[namespace] = url
  
          if self.skip_validation:
              return tokens
  
          namespace_result = self.manager.get_or_create_namespace(url)
  
          if isinstance(namespace_result, dict):
              self.namespace_to_term[namespace] = namespace_result
              self.uncachable_namespaces.add(url)
          else:
              self.namespace_to_term[namespace] = self.manager.get_namespace_encoding(url)
  
          return tokens